Signal translating and correcting system



June 11, 1935. H. G. TASKER 2,004,253

SIGNAL TRANSLATING' AND CORRECTING SYSTEM Filed April 20, 1932 FlG.i

' S E FIG. 3

U E Q FIG. 2 z TRANSFORMER CHARACTERISTICS f '5, U i Z 0 Q CELL CHARACTERISTICS! 0- Z S u.| O! (D g FREQUENCY & I .23 g CHARACTERISTICS DUE TO SHUNTING x q: EFFECT OF RESONANT CIRCUIT FREQUENCY E Q at: V

FIG.5 a I LIJ FI 6.4 m -J g a FREQUENCY 1- 4 =3 FIG. 6 Z COMBINED cHAIzAcTEmsms E commas CHARACTERISTICS OF czu. OF CELL AND TRANSFORMER E TRANSFORMER AND RESONANT CIRCUIT 2 g 1 v w 3 W n G a I M FREQUENCY FREQUENCY INVENTOR flower 6. 7&5/(er BY ATroRNEY 1 invention relatesto signal systemsgand, particularly; to means for amplifying not' strictly linear, *but-ishows a maximum at' ap 4 Patented June 11, 1935 simian Tm" Afivwmma 1.11am c po a i n 9 l o-v1 D aw e andequalizing the response of a signal transl tr iIIQsystem plicity and: low cost thereof; :Difliculty is;. hovvr even; experienced with? the selenium; cell -as; well aswother? types of cells in :that i the responselof the" cell is not proportionalto, but varieswithg-the freqquency of the, incident-light pulsationsfrom the optical record, in .theselenium cell; thefresponse; beingmuch greater at lowjpfrequencies than at object 'ofthis invention is to equalize; and compensatekfor; the deviations from proportione ality of response ofa light sensitivecell to changes in; frequency of modulated light of constant am -l vplitudes Anothenobjectiis to modify fohe characteristic response' curve of-aselenium cell reproducings'ys l temto: obtain substantially linear response :over. a

for the; preponderantrresponsepica selenium oell wide range of frequencies. {I

, It has been found possible means ofr' a-g-transformer having alow inductance;

tolow-frequencies, of modulated-light'from an ,optical record; but t-he resulting response curve; is

point near the middle of the usefjul; frequency range -that is; between 500 and 2,000 vibrations \Thisinventi'on provides a simple-auxiliary cuit, which flattens the maximum of the'charac teristiecurve and produces substantially alinear proportionalreproduction over a wide-range of fre ing the frequency response of a selenium cell attenuatingthe low.- frequency response thereof-t a; value appropriate to the higher. frequency re' p nse thereof, auxiliary, means being provided for attenuating. the middle, frequency response The 1' reproduction ofoptical} record is conveniently done by. means of "a light sensitive circuit such-as": a

I more than one may compensate;

of various members ofzthef system. i Referring to: thegcfigures, an exciter, light ljgis provided; ooop'e'ratingg through suitable devices to 1 illuminate an optical sound record 2;'which record 76.?

servesrtomodulat'eg light from the exciter light l,

nectedto ancaniplifier tube 6, as 'shown; which; in turn; connected to a ntransformerv 1, as indicated. The transformer I .desirablysupplies a second fv'acuuin tube 8;. which iscoupled toa third.

vacuum tube l l whichis adapted to supply a load loudspeaker; or other translate ingideviceflg i a y It is; of course, obvious-that the number of vac-; uum tubes andxtiansforniei's may be" varied according toathe needs 'of the Joadcircuitj and that be oflow inductanceas before described; v p

The transformer 1 is desirably. one or low impedance, to attenuate the pulsatingcurrentscore responding to thelow .vibrationfrequenciesa in the record; 2.5more than 'itattenuates'the higher frequenbiesfrom the record 2', as disclosed in the co'epending application of .John' Nielsen, Serial Number {6063.94, 1fi1ed April 20, .1932; s

'Conn'ected in shunt tothe primary coil of *the transformer 'l is 'a series resonant circuit, consistingof an inductance-l4; a condenser l5 and a; resistance l6. q l se e i misen has a 'i e r s qh echaracteristic of the type shown in Fig. .2. Itv

that the response issuificiently great at vibration frequencies as; high asaooo cyclesto beusable, andincreasestoanumber -Theinvention; therefore, provides for -correctat value at 1owi f'requencies, such as.

fieris shown'in Fig.4. 4 it y l The seriesresonan't circuitis designedby adflii'stiiient of the" inductance and capacity tozjhave a"""riatural resonant response point, coinciding with the "maximum indicated in' Fig; 4, as shown The-resulting response characteristic of 1 the coni-bination of cell, transf'ormerand ampliationsper second. The transformer"! ntiohedfNielsem application, and has a for th resonant circuitin Fig. 5. H'Iheresistance is adjustedwto broaden the resonant peak by an appropriate amounts The; effect of the series plitude optical record over this range of fre-.

quencies.

In the operation of the device and method of this invention, the exciter light provides a steady beam of light, which is modulatedby the optical record 2, converted by the cell 3 into electrical vibrations, which are corrected bythe transformer I to equalize the frequency response at the high and low ends of the useful frequency spectrum; which pulsations are then further corrected by the series resonant circuit to equalize the middle frequencies to those at thetop and bottom of the frequency range; i

In the embodiment shown in Fig. 1 the" desired correction of the curve at the midpoint isobtained by the use of a series resonant circuit connected in shunt to the coupling transformer, and is the preferred form, since it introduces a minimum of-losses in the circuit; Similar results can; however, be obtained by'the use of a parallel resonant circuit, consisting of an inductance connected between the plate of the tube 6 and the primary of the transformer 1, the inductance'being shunted by a condenser to form a'parallel resonant circuit with a resistancein series either withthe inductance or the condenser to broaden the resonant peak. This construction imposes agreater impedance to the transfer of pulsations from the. tube 6 at points near its natural resonant frequency, which is desirably adjusted to match the maximum of the characteristic curve of Fig. 4. This system, however, is less desirable because of the greater losses encountered therein.

The preferred embodiment of the invention utilizes but a single auxiliary resonant circuit, since in most cases but a single maximum is encountered in the characteristic curve. If, however, equalization of the high and low frequencies is obtained in two steps as described in the above mentioned Nielsen application, the equalization of themiddlefrequencymay also conveniently be performed in two steps, thereby permitting the system to compensate for two maxima if such should occur. a

By the device of this invention there is thus obtained a more uniform response in electrical vibrations from an optical sound record by a simple, convenient and inexpensive light cell and amplifier system. p I

While there is herein disclosed but a single embodiment of the device of this invention, it is possible to produce still other embodiments thereof without departure from the inventive concept herein disclosed, and it is, therefore, desired that only such limits shall be imposed upon the appendedclaims as are stated therein or required by the prior art. r

i The invention claimed is:

1; In combination, a light responsive cell, means for attenuating the low frequency response thereof to a value appropriate to the higher frequency response thereof, and auxiliary means for attenuating the middle frequency response to correspond to the high and low frequency response,

said auxiliary means comprising a condenser, 21. reactance and a resistance connected in series.

2. In combination, a light sensitive cell mem ber, a transformer connected thereto, a vacuum tube amplifier supplied therefrom, a second transformer having low inductance supplied therefrom, a series resonant circuit ,connected therewith, damping ,means in said resonant circuit for modifying the transmission character .istic over a wide range of frequencies, a third transformer, also of low impedance, an associated vacuum tube,fland an output circuit.

3. In combination, a light sensitive cell member, a transformer connected thereto, a vacuum tube amplifier supplied therefrom, a second transformer having low inductance supplied therefrom, and a series resonant circuit connected in shunt with said second transformer, said series resonant circuit comprising an inductance, a capacitance, and a damping resistance.

'4. In'combination, a selenium cell having an inherently greater responseto low frequencies'of' modulated light than to higher frequencies, 'an amplifier member connected thereto, means comprising a transformer adapted to attenuate the low frequency response of said cell to an ampli tu'de'level corresponding to the higher frequency response, and an auxiliarynieans cooperating therewith for attenuating the middle frequency response to correspond to the high and low fre-' quency' response, said auxiliary means comprising a condenser, an inductanceand a damping resistance connected in series. I

5. In combinationQa' selenium cell having an inherently greater response to low'frequencies of modulated light than to higher frequencies,

an amplifier member connectedthereto, means comprising a transformer adapted to attenuate the low frequency response of said cell to an amplitude level corresponding to the higher fre'-' quency response, and an auxiliary means cooperating therewith for attenuating the middle frequency response to correspondtothehigh and low frequency response, said auxiliary 1 means comprising a series resonant circuit anda damp,- ing resistance therein. i e

6. In combination, a light responsive cell, means for attenuating the response thereof at a low frequencyto avalue appropriate to the re'-- sponse thereof at a high freduericmfauxiliary means for attenuating the responseibetween said low frequency and said high frequency,said auxiliary means comprising capacity, inductance and resistance connected in series whereby the fre-' quency response is made substantially uniform between the said low frequencyand thesaid high frequency. V, f e e f '7. In combination, a 'light responsive cell, means for attenuating the responsethereof at a" low frequency to a value appropriate to the response thereof at a high frequency, shunt aux: iliary means for attenuating response between said low frequency and said high frequency, said shunt auxiliary means comprising capacity, inductance and resistance connected in series whereby the frequency response is made substantially uniform between the said low frequency and the said high frequency. 7 v 1 v 8. In combination, a selenium cell having an inherently greater response .to low frequencies of modulated light than to higher frequencies, a cir cuit connected thereto'comprising an amplifier and means comprising a transformer adapted to attenuate the low frequency response of said tude level corresponding to the higher frequency response, and an auxiliary means in shunt to said output circuit of said amplifier for attenuating 3 her having an output circuit and means comprising a transformer adapted to attenuate the i low frequency response of said cell to an amplithe middle frequency response to correspondto,

the high and low frequency response, said auxiliary means comprising a series resonant circuit I and a damping resistance therein. a

t HOMER G. TASKER. 

